1. Field of the Invention:
The present invention relates to a NOISE REDUCTION APPARATUS for reducing noise of video signals for use in a video signal recording/reproducing system such as a video tape recorder and the like.
2. Description of the Prior Art:
The video tape recorders (VTR) which are extensively used in general in recent years are provided with various noise reducing circuits in order to reduce noises which are mixed in reproduced luminance signals.
A typical one of such circuits is to take out a high-frequency component including noise from an input signal, limits the amplitude of it with a limiter, and substracts the amplitude-limited high-frequency component from the input signal. By this circuit, noise component of small amplitude is reduced without deteriorating high-frequency signal component which was a large amplitude. That is to say, without deteriorating the horizontal resolution of the image, noise on the flat area can be reduced.
However, when, for example, there is a sharply rising vertical line image on an image, the signal portion to represent this vertical line image is subjected to amplitude limitation by the limiter, so that it is impossible to reduce the noise at this portion, and eyesore noise remains.
For reducing such noise at the vertical line image portion of the image, there is a circuit so designed as to take out a high-frequency component of vertical frequency of the image from the input signal, limits its amplitude, and subtract it from the input signal (U.S. Pat. No. 4,302,768). When this circuit is used, because the signal portion representing the vertical line image does not include the high-frequency comnponent of vertical frequency, only the noise component passes through the limiter, so that there is a possibility to reduce the noise at this portion.
In fact, however, because the amplitude of the noise component of the high-frequency region of vertical frequency at the vertical line image portion is relatively large, the noise component does not fully pass through the limiter, and thus it is not possible to reduce sufficiently this sort of noise. When the passing amplitude of the limiter is enlarged so as to reduce this sort of noise, the vertical resolution of the image is inevitably deteriorated.